output error

** (EXIT from #PID<0.80.0>) an exception was raised:
    ** (FunctionClauseError) no function clause matching in HashDict.dict_delete/2
        (elixir) lib/hash_dict.ex:90: HashDict.dict_delete([], "milk")
        (elixir) lib/hash_dict.ex:68: HashDict.pop/3
        (elixir) lib/agent/server.ex:20: Agent.Server.handle_call/3
        (stdlib) gen_server.erl:607: :gen_server.try_handle_call/4
        (stdlib) gen_server.erl:639: :gen_server.handle_msg/5
        (stdlib) proc_lib.erl:237: :proc_lib.init_p_do_apply/3

Interactive Elixir (1.1.0-dev) - press Ctrl+C to exit (type h() ENTER for help)

03:12:36.665 [error] GenServer :shopping terminating
Last message: {:update, #Function<0.4009554/1 in KV.Bucket.put/3>}
State: []
** (FunctionClauseError) no function clause matching in HashDict.dict_delete/2
    (elixir) lib/hash_dict.ex:90: HashDict.dict_delete([], "milk")
    (elixir) lib/hash_dict.ex:68: HashDict.pop/3
    (elixir) lib/agent/server.ex:20: Agent.Server.handle_call/3
    (stdlib) gen_server.erl:607: :gen_server.try_handle_call/4
    (stdlib) gen_server.erl:639: :gen_server.handle_msg/5
    (stdlib) proc_lib.erl:237: :proc_lib.init_p_do_apply/3